The present invention relates to measurement of the temperature of motor windings, and more particularly to the determination of the temperature by measuring the resistance of the winding.
It is frequently necessary or desirable to determine the temperature of a motor winding, for protection or other purposes, and it is often desired to monitor the winding temperature continuously so that the motor can be deenergized or other appropriate action taken if the temperature exceeds a safe value. Various means have been used for this purpose such as thermistors or other temperature detectors placed on the motor windings to respond directly to the temperature, or current responsive devices for tripping the motor circuit breaker in response to excessive current which would produce overheating if allowed to continue. Since motor windings normally consist of copper conductors, with a positive temperature coefficient of resistance, the temperature of the winding can also be determined by measuring the resistance, but this method of temperature detection has not heretofore been used because of various practical difficulties in measuring the resistance, especially on a continuous basis during operation of the motor.